The subject matter of the invention is a catalytically operating method for the production of organosilicic ester compounds of the general formula I, EQU R.sub.a SiX.sub.n (OR').sub.4-a-n (I)
which contain 1 to 3 halide moieties X in addition to alkoxy groups (OR') (n=1 to 3) and (4-a-n).gtoreq.1, and also, in some cases, a maximum of 2 substituents R (a=0 or 1 or 2) which can be hydrogen, alkyl groups (substituted with halogen if desired), alkenyl groups and/or aryl groups (substituted with halogen and/or alkyl). The ester groups --OR' are formed from primary or secondary alcohol moieties whose organic grouping R' consists in each case of a saturated and/or unsaturated, in some cases branched, alkyl group having 1 to 8 carbon atoms, which if desired can also contain ether oxygen functions. The partial esters of formula I obtained according to the claimed method therefore contain at least one R'O moiety, so that the sum of a +n can assumes values of 1, 2 or a maximum of 3. Formerly, these partial esters were made exclusively by esterifying chlorosilanes with less than stoichiometric amounts of alcohols. In this method, whenever monoesters were the object, considerable excesses of chlorosilanes had to be used in order to suppress insofar as possible the rate of formation of the undesired but unavoidably formed higher esterification stages. Nevertheless, even when the starting chlorosilane is in a three-fold to four-fold excess, it is not possible to achieve a monoester-to-diester ratio better than 2:1 to 3:1 (cf., e.g., K. A. Andrianov et al., J. Gen. Chem. USSR 26, 207 to 209, 1956; also Zhur. Obsh, Khim 20, 3754 to 3757, 1959; also USSR-Pat. No. 130891). The situation is still more complicated in the case of the production of diesters or triesters on account of the additional occurrence of other undesired stages of esterification. The disadvantages of this conventional procedure lie mainly in the exacting measures to be taken in distilling the pure product, and particularly in the excessively low yields of the desired degree of esterification. Attempts have therefore also been made to equilibrate esters of the general formula EQU R.sub.a Si(OR').sub.4-a
with chlorosilanes in the presence of hydrogen chloride (cf. Brit. Pat. No. 653,238; M. Kumada, J. Inst. Polytechn. Osaka Univ., Ser. C, 2, 139 to 146, 1952), but only the same disadvantageous results as referred to above were achieved. In addition a beside reaction takes place forming ethers (R'OR') and polysiloxanes followed by becomming instable and by complete destruction of the product. Therefore this process is not in large scale application. Esterification experiments using pyridine as acid accept or have delivered the target product to a greater degree, but with still unsatisfactory yields. The special disadvantage of this method is the unavoidable production of undesired pyridine hydrochloride in a large amount, resulting in high costs (cf. U.S. Pat. No. 2,927,938).
Accordingly, for the better utilization of the starting substances, the problem existed of finding a method of production suitable for technical application, according to which the desired compounds of the general formula I will be obtained in a very direct manner, and the yield of by-products will be very low, and in which even mixtures of halogen silane partial esters can be used as starting products for the production and separation of a defined partial ester to a predominant degree.